It is proposed to study the biochemical and functional changes in various tissues of rats made thiamine-deficient by thiamine deprivation and treatment by thiamine antagonists and by various types of stress. Also to study the factors affecting the requirements for thiamine and the conversion to the active coenzyme and dephosphorylation to the inactive forms. Studies will be made of the enzyme dephosphorylation to the inactive forms. Studies will be made of the enzymes responsible for the oxidative decarboxylation of alpha-ketoacids other than pyruvate and alpha-ketogluatarate, especially of the branched-chain ketoacids due to their significance in Maple Syrup Urine Disease. In this connection, the presence and levels of these ketoacids will be studied in blood and tissues under a variety of conditions. Studies will also be continued on the biochemical disturbance responsible for the neurological, heart and anorexic symptoms of thiamine deficiency.